37
To adjust an alarm setpoint, select 'SPx1' or
'SPx2' and press
P
which will reveal the current
setting. Each digit of the setpoint may be
adjusted using the
Up
and
Down
push-buttons,
and the
P
button to move control to the next digit.
When the required setpoint has been entered,
pressing
E
will return the display to the 'SPx1' or
'SPx2' prompt from which the other setpoint may
be selected, or the instrument may be returned to
the display mode by pressing
E
again.
Note:
Direct access to the alarm and control
output setpoints is only available when the menu
is enabled - see section 2.6.10
2.7 OPTIONAL 4/20mA OUTPUT
The BA364D can be supplied with an optional
4/20mA output which may be programmed to
produce an analogue output proportional to the
whole or part of the total or rate display. See
section 1.9.7.1 for intrinsic safety details.
2.7.1 Programming and adjustment
The main counter programme menu is extended
as shown in Fig 2.6 to accommodate the 4/20mA
calibration functions.
The ‘4-20 OP’ programme function allows the
4/20mA output current to correspond to any
positive total or rate display. e.g. 4mA could
represent 0 counts and 20mA 5000 counts.
Note:
Negative display numbers can not be
represented by the 4/20mA output.
To calibrate the 4/20mA output current, enter the
programme mode by operating the
P
and
E
push-
buttons simultaneously. Using the
Up
or
Down
push-button select the function ‘4-20 OP’ and
press
P
which will result in the BA364D
displaying the first sub-menu function ‘4.000’. –
See Fig 2.6. Using the
Up
or
Down
push-button
select the ‘4-20 tYPE’ function which enables the
4/20mA output to be controlled by the total or rate
display. Press
P,
select the required source and
then return to the sub-menu by pressing the
E
button.
The displayed values which correspond to 4mA
and 20mA output may now be defined. Using the
Up
or
Down
push-button select the ‘4.000’
prompt for the function which defines the display
at which the output current will be 4.000mA.
Press
P
to reveal the existing setting with the
most significant digit flashing. The decimal point
will be fixed in the position already defined for the
display by the ‘d.P’ function. The value of the
flashing digit may be changed by pressing the
Up
or
Down
buttons. When this digit is set as
required, pressing
P
will transfer control to the
next digit.
When the required display has been entered,
press the
E
button to return to the ‘4.000’ prompt.
To enter the display at which the output current
will be 20.000mA, press the
Up
or
Down
button
to select the ’20.000’ prompt followed by
P to
reveal the current setting, which may be changed
in the same way as the 4mA setting. When
adjusted as required, press
E
three times to
return to the display mode via the ‘20.000’ and ‘4-
20 OP’ prompts.
The 4/20mA output may be calibrated to increase
or decrease as the display increases, and most
instruments will produce a linear output between
3.5 and 22mA.
Fig 2.6 4/20mA output programme structure
Note:
If the counter display calibration is
changed by adjusting the scale factors, timebase
or the position of the displayed decimal point, the
4/20mA output will automatically be set to give a
constant 3.5mA output irrespective of the total or
rate display. The 4/20mA output must therefore
always be recalibrated following recalibration of
the counter.
